Problem: 7 crayons cost $10.85. Which equation would help determine the cost of 11 crayons?
Explanation: There are several equations that could help determine the cost, each with a slightly different approach. We know the cost of 7 crayons. We want to know the cost of 11 crayons. We can write the numbers of crayons as a proportion: $\dfrac{7}{11}$ We know 7 crayons costs $10.85. We can let $x$ represent the unknown cost of 11 crayons. The proportion of these costs can be expressed as: $\dfrac{\$10.85}{x}$ The cost changes along with the number of crayons purchased, and so the two proportions are equivalent. $\dfrac{7}{11} = \dfrac{\$10.85}{x}$